Method and apparatus for communicating control data in an asynchronous communications channel

ABSTRACT

A communication system communicates control data in unused segments in the data stream of an asynchronous channel. The communication system includes a transmitting unit and a receiving unit. The transmitting unit transmits communications data to the receiving unit via the asynchronous channel, in compliance with the channel&#39;s asynchronous protocol. However, the transmitting unit transmits control data to the receiving unit in unused segments of the data stream.

FIELD OF THE INVENTION

The field of invention relates to communication systems in general; and,more specifically, to control data communication in an asynchronouschannel.

BACKGROUND

Many communication systems asynchronously communicate data over acommunications channel. For example, in many network applications, thecommunication channel is designed to comply with the IEEE std.802.3-2000, published October, 2000. Although the IEEE 802.3 standard(also referred to herein as the Ethernet standard) is in wide use, thereare many other asynchronous communications channels such as, forexample, Asynchronous Transfer Mode (ATM), Packet over SONET (POS),Token Ring, and Fiber Channel.

Transmitter, receiver and/or transceiver units used in suchcommunication systems often communicate control data (includingdiagnostic, synchronization and configuration, and other types of dataused in managing the units) among each other. In many conventionalcommunication systems, this control data is communicated in the samemanner as normal communications data. For example, in an Ethernetchannel, the control data would be communicated using data frames thatcomply with the Ethernet standard. As a result, each data frame used totransfer control data cannot be used for normal communications data,thereby reducing the effective bandwidth of normal communications data.

SUMMARY OF THE INVENTION

In accordance with aspects of the present invention, a communicationsystem is provided that communicates control data in unused segments inthe data stream of an asynchronous channel. The communication systemincludes a transmitting unit and a receiving unit. The transmitting unittransmits communications data to the receiving unit via the asynchronouschannel, in compliance with the channel's asynchronous protocol.However, the transmitting unit transmits control data to the receivingunit in unused segments of the data stream.

In another aspect of the present invention, the asynchronous channel isan Ethernet channel, with the unused segments being the inter-frame gap(IFG) specified in the Ethernet standard.

In still another aspect of the invention, the unused segments are idlesegments in the data stream. For example, if the channel is an Ethernetchannel, the transmitting unit may be controlled to transmit “idleperiods” as specified in the Ethernet standard. The transmitting unitcan detect such idle periods and insert control data in the dataportions of the frame. In some embodiments, control data can be insertedin both IFGs and idle periods.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a block diagram illustrating a basic communication system,according to one embodiment of the present invention.

FIG. 2 is a flow diagram illustrating the operational flow of thecommunication system of FIG. 1.

FIG. 3 is a block diagram illustrating a communication system with afree space optical link, according to one embodiment of the presentinvention.

FIG. 4 is a diagram illustrating an inter-frame gap of an Ethernetchannel.

FIG. 5 is a flow diagram illustrating the operational flow of thecommunication system depicted in FIG. 3, according to another embodimentof the present invention.

FIG. 6 is a flow diagram illustrating the operational flow inmultiplexing control data in idle periods in an Ethernet data stream.

FIG. 7 is a block diagram illustrating a transceiver as depicted in FIG.3, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a basic communication system 10, according to oneembodiment of the present invention. In this embodiment of theinvention, communication system 10 includes a transmitter 12 and areceiver 13. In addition, communication system 10 can include acompliant device 14 (or several compliant devices). Transmitter 12 andreceiver 13 communicate over a channel 15 that is asynchronous. Forexample, channel 15 may support communication according to theaforementioned IEEE 802.3 standard or other CSMA (carrier sense multipleaccess) or CSMA/CD (CSMA/collision detection) protocols, including olderversions and likely updates to the Ethernet standard.

In one embodiment, transmitter 12 and receiver 13 are free space optical(FSO) units. In other embodiments, transmitter 12 and receiver 13 maycommunicate over any suitable wired or wireless media. Transmitter 12and receiver 13 include controllers 16 and 17, respectively. Inaccordance with the present invention, controllers 16 and 17 areconfigured so that transmitter 12 and receiver 13 can exchange controldata by multiplexing portions of the control data in unused segments inthe data stream. In some embodiments, these control data exchanges neednot fully comply with the all off the requirements of the protocol. Forexample, when channel 15 is an Ethernet channel, the control dataportions may be inserted in the inter-frame gap (IFG) or following anidle pattern, which are both specified in the aforementioned Ethernetstandard.

Compliant device 14 is a device that communicates with receiver 13 viaan asynchronous channel 18. In this optional embodiment of communicationsystem 10, communications between compliant device 14 and receiver 13should fully comply with the protocol being used for channel 18. In someembodiments, channels 15 and 18 use the same protocol or standard (e.g.,Ethernet), although in other embodiments channels 15 and 18 may usedifferent protocols or standards.

FIG. 2 illustrates the operational flow of communication system 10 (FIG.1). Referring to FIGS. 1 and 2, communication system 10 operates asfollows according to one embodiment of the present invention.

In basic operation, transmitter 12 transmits a data stream to receiver13 via channel 15. In particular, transmitter 12 transmits normalcommunications data according to the protocol or standard of channel 15.Receiver 13 receives the data stream and extracts the embeddedcommunications data. Because the protocol of channel 15 is asynchronous,the data stream will have segments that are unused (also referred toherein as idle periods).

These unused segments in the data stream are then detected. In oneembodiment, transmitter 12 detects such unused segments in the datastream. For example, in an Ethernet embodiment, controller 16 oftransmitter may be configured to monitor frames in the data stream foridle patterns. In another embodiment, controller 16 detects the end of aframe (i.e., the beginning of an IFG). This operation is represented bya block 21.

If there is control data to transmit to receiver, some control data isinserted in the data stream via an unused segment. In one embodiment,transmitter 12 multiplexes some control data in an unused segment,between frames containing communications data. Continuing the Ethernetexample above, controller 16 may be configured to multiplex control datainto (a) the IFG following a frame containing communications data;and/or (b) into a segment following the detection of an idle pattern (orthe detection of N consecutive idle patterns, where N represents aninteger greater than one). This operation is represented by a block 23.

The control data is then extracted from the data stream in receiver 13.In one embodiment, controller 17 is configured to detect control datathat is inserted in the data stream. For example, in an Ethernetembodiment, controller 17 may be configured to detect data inserted inthe IFG. Alternatively or in addition, controller 17 may be configuredto detect an idle pattern and extract the control data, if any, thatfollows the idle pattern. In this embodiment, receiver 13 then processesthe extracted control data as is commonly done in conventional systems.This operation is represented by a block 25.

The communications data is extracted from the data stream. In thisembodiment, controller 17 is configured to extract the communicationsdata from the data stream. In the embodiments having compliant device14, receiver 13 passes the communications data to compliant device 14via channel 18. As previously described, communications over channel 18fully comply with the protocol of channel 18. For example, channel 18may also be an Ethernet channel. Receiver 13 would transmit theextracted communications in compliance with the Ethernet standard (e.g.,with the IFG restored and having no control data). This operation isrepresented by a block 27. The operational flow then returns to block21.

Although FIG. 2 shows the operations as being sequentially performed inthe indicated order, the operations can be performed in differentsequences. For example, the operations of blocks 21 and 23 are performedessentially independently of blocks 25 and 27. Thus, for example, one ormore iterations of blocks 21 and 23 may be performed to communicatecontrol data before blocks 25 and 27 are performed in which the controldata is extracted. For example, receiver 13 may receive the control dataand buffer it before processing the control data.

FIG. 3 illustrates a communication system 30 with a free space optical(FSO) link, according to one embodiment of the present invention. Inthis embodiment, communication system 30 includes a network 31, atransceiver 12A, a transceiver 13A and another network 14A. Transceivers12A and 13A include controllers 16A and 17A, respectively. Communicationsystem 30 is an expansion of communication system 10 (FIG. 1) in thattransmitter 12 and receiver 13 are expanded to transceivers (i.e.,transceivers 12A and 13A), and compliant device 14 is expanded to anetwork (i.e., network 14A). These transceivers provide a link betweennetworks 31 and 14A.

The elements of communication system 30 are interconnected as follows.Network 31 is connected to transceiver 12A via a channel 33, which iswired in this embodiment. Transceiver 12A is connected to transceiver13A via FSO channel 15A. Although in this embodiment channel 15A is aFSO link, in other embodiments channel 15A may be implemented in anysuitable media (e.g., optical fiber, twisted pair, RF, cable, etc.).Transceiver 13A is also connected to network 14A via a channel 18A,which is a wired channel in this embodiment. In this exemplaryembodiment, channels 33, 15A and 18A and networks 31 and 14A all complywith the Ethernet standard. In other embodiments, these channels andnetworks may use any suitable asynchronous protocol or standard.Basically, transceivers 12A and 13A function as devices on networks 31and 14A, respectively.

In application, communication system 30 can be used, for example, tolink a network in one location to a network in another location. Channel15A supports FSO communication between networks 31 and 14A viatransceivers 12A and 13A.

As previously described, the Ethernet standard specifies a minimumspacing between frames commonly referred to as the IFG). FIG. 4illustrates an IFG of an Ethernet channel. More particularly, when atransmitting unit transmits a frame 41, the Ethernet standard specifiesthat the next frame 42 can only be transmitted after IFG 43 hastranspired. The IFG is currently specified as the time needed totransmit 96 “bits” over the channel. As will be described in more detailin conjunction with FIG. 5, a transmitting unit may transmit controldata in IFG 43.

FIG. 5 illustrates an operational flow of communication system 30 (FIG.3), according to an embodiment of the present invention. Referring toFIGS. 3 and 5, communication system 30 operates as follows incommunicating control data between transceivers 12A and 13A during IFGs.

Communications data is received by a transceiver from a device in thenetwork connected to the transceiver. For example, a device in network31 can send communications data that is intended for a device in network14A. This communications data is received in an Ethernet compliant frameby transceiver 12A, via channel 33. This operation is represented by ablock 51 in FIG. 5.

The communications data is transmitted to the other transceiver (i.e.,receiving transceiver in this example communication exchange) overchannel 15A. Control data, if any, is inserted in the IFG following theframe of communications data. Continuing the above example, thecommunications data received by transceiver 12A is transmitted totransceiver 13A via FSO channel 15A in an Ethernet compliant frame.

In addition, if transceiver 12A has control data to send to transceiver13A, transceiver 12A may add the control data to the data stream byinserting at least a part of the control data in the IFG following theframe of communications data. In one embodiment, transceiver 13A detectswhen IFGs occur by detecting idle periods (as described, for example, inconjunction with FIG. 6). Although this communication exchange may beinconsistent with the Ethernet standard, this inconsistency istransparent to devices on networks 31 and 14A. This operation isrepresented by a block 52.

The communication and control data is received by the receivingtransceiver via FSO channel 15A. Continuing the above example,transceiver 13A receives the communications data in an Ethernetcompliant frame and the control data in the following IFG. Thisoperation is represented by a block 53.

The control data is then extracted from the received data. In the aboveexample, transceiver 13A extracts the control data from the IFG andprocesses it in accordance with a predetermined set of rules. Thisoperation is represented by a block 54.

The communications data is then transmitted to the network containingthe device to receive the communications data. Continuing the aboveexample, transceiver 13A then transmits the communications data tonetwork 14A via channel 18A, in an Ethernet compliant frame. Transceiver13A then waits unit the IFG transpires before sending another frame.Thus, in accordance with the present invention, the communication ofcontrol data between transceivers 12A and 13A is transparent to deviceson networks 31 and 14A. This operation is represented by a block 55.Although block 55 is shown in FIG. 5 as being performed before block 54,a transceiver can perform these operations essentially in parallel. Theoperational flow returns to block 51 so that one of the transceivers canreceive a next frame of communications data.

FIG. 6 illustrates the operational flow of communication system 30 inmultiplexing control data in idle periods in an Ethernet data stream,according to one embodiment of the present invention. Referring to FIGS.3 and 6, communication system 30 performs this operation as follows. Atransceiver receives Ethernet encoded data from a device in the networkto which the transceiver is connected. For example, transceiver 13A mayreceive Ethernet encoded data from a device of network 14A. Thisoperation is represented by a block 61.

The received data is monitored to determine whether the received datacomprises an Ethernet compliant idle period. Continuing the aboveexample, transceiver 13A checks the code words (specified in theaforementioned IEEE 802.3 Standard) of the received data for the patternassigned to an idle period. More specifically, the code words are partof a five-bit/four-bit coding scheme that indicates the nature of thedata. In the current Ethernet standard, the five-bit code word for anidle period is defined by the five consecutive bits “11111”. Thus, inthis example, transceiver 13A monitors the data stream to detect when adevice of network 14A sends data to transceiver 13A that isrepresentative of an idle period. Communication system 30 can alsosupport control data flow in the opposite direction using this idleperiod technique. This operation is represented by blocks 62 and 63.

If an idle period is detected, control data is inserted in the idleperiod. Continuing the above example, if transceiver 13A detects an idlepattern in the data, transceiver 13A inserts a portion of control data(e.g., a word) in the space occupied by the idle period. Transceiver 13Athen transmits this data to transceiver 12A via FSO channel 15A. Thisoperation is represented by a block 64.

In an alternative embodiment, the transceiver waits for two consecutiveidle patterns (or any preselected number of consecutive idle patterns)before inserting control data in the space occupied by an idle period.In this way, a byte of control data is sent to the other transceiver.

However, if in block 63, an idle pattern in not detected, thecommunications data is transmitted in an Ethernet compliant frame overchannel 15A. Continuing the above example, transceiver 13A wouldtransmit the communications data received in block 61 to transceiver 12Avia FSO channel 15A in Ethernet compliant data symbols. This operationis represented by a block 65. The operational flow then returns to block61 to allow a transceiver to receive a next segment of communicationsdata from one of the networks.

FIG. 7 is a block diagram illustrating an implementation of transceiver12A (FIG. 3), according to one embodiment of the present invention.Transceiver 13A (FIG. 3), in one embodiment, is essentially identical inhardware implementation to this embodiment of transceiver 12A. Referringback to FIG. 7, in this embodiment, transceiver 12A includes an Ethernetinterface 71, a traffic control processor 72, a management processor 73,a memory 74 and an optical interface 75. Traffic control processor 72,management processor 73 and memory 74 form part of controller 16A (FIG.3).

Ethernet interface 71 is the physical layer interface that is configuredto receive Ethernet data from an Ethernet channel and place it in a formthat is usable by transceiver 12A. In addition, Ethernet interface 71 isalso configured to take data from transceiver 12A and transmit it overthe Ethernet channel in a format compliant with the Ethernet standard.

Traffic control processor 72 is a processor configured to process and/orcontrol the flow of communications and control data in and out oftransceiver 12A. Management processor 73 is a processor configured tocontrol diagnostic and other control functions of transceiver 12A (i.e.,functions separate from the handling of communications data to and fromchannels 33 and 15A). In some embodiments, a single microprocessor ormicrocontroller device may be used to implement both traffic controlprocessor 72 and management processor 73.

Memory 74 includes memory devices such as, for example, random accessmemory (RAM) devices and non-volatile memory devices to store data,configuration information, programs, instructions, etc. used by theprocessors 72 and 73, as is common in computers and computer controlledsystems.

Optical interface 75 is a physical layer interface that is configured toreceive Ethernet data from a FSO channel and place it in a form that isusable by transceiver 12A. In addition, optical interface 75 is alsoconfigured to take data from transceiver 12A and transmit it over theFSO channel (in Ethernet compliant data symbols in this embodiment).

The elements of this embodiment of transceiver 12A are interconnected asfollows. Ethernet interface 71 is connected to channel 33 and to trafficcontrol processor 72 via a line 76. Traffic control processor 72 isconnected to management processor 73 and memory 74 via a line 77, and tooptical interface 75 via a line 78. Management control processor 73 isalso connected to memory 74 via line 77. Optionally, Ethernet interface71 is connected to traffic control processor 72 via a line 79. The term“line” as used in this context can refer to multiple lines (e.g., a bus)as well as a single line.

TRANSCEIVER OPERATION

Transceiver 12A handles the flow of data from channel 33 to FSO channel15A as follows. Communications data from network 31 (FIG. 3) is receivedby Ethernet interface 71 via channel 33 and provides the communicationsdata to traffic control processor 72 via line 76.

Ethernet interface 71 monitors incoming data from channel 33 for idlepatterns (e.g., as described above in conjunction with FIG. 6). IfEthernet interface 71 detects a preselected number of consecutive idlepatterns (which can be a single idle pattern in some embodiments),Ethernet interface 71 sends an interrupt signal to traffic controlprocessor 72 via line 79.

Traffic control processor 72 provides the communications data to opticalinterface 75 via line 78. In addition, traffic control processor 72inserts control data, if any, received from management processor 73 tobe transmitted to transceiver 13A via channel 15A in unused segments ofthe data stream. For example, management processor 73 can providecontrol data as previously described in conjunction with FIGS. 3–5.

In one embodiment, control data from management processor 73 can bestored in a cache integrated on the processor device implementingtraffic control processor 72. Thus, traffic control processor 72 cancheck to see if the cache is populated (thereby indicating that there iscontrol data to be transmitted) and sends a signal to Ethernet interface71 to monitor incoming data from channel 33 for idle patterns.

Optical interface 75 then generates an optical signal that encompassesthe Ethernet communications and control data provided by traffic controlprocessor 72. This optical signal is transmitted to transceiver 13A viaFSO channel 15A.

Transceiver 12A handles the flow of data from FSO channel 15A to channel33 as follows. Data received via channel 15A can include communicationsdata from network 14A (FIG. 3) via transceiver 13A. In addition, thisdata may include control data from transceiver 13A. Transceiver 13Atransmits this communications and control data over FSO channel 15A inessentially the same manner as described above for transceiver 12A.

Communications data from network 14A (FIG. 3) is received by opticalinterface 75 via channel 15A. Optical interface 75 provides thecommunications and control data to traffic control processor 72 via line78.

Traffic control processor 72 extracts the communications data andprovides it to Ethernet interface 71 via line 76. In addition, trafficcontrol processor 72 extracts control data, if any, and provides it tomanagement processor 73 via line 77. Management control processor 73 canthen perform diagnostic or other management or control functions inresponse to this control data.

Ethernet interface 71 receives the extracted communications data fromtraffic control processor 72 and transmits this communications data viachannel 33 in Ethernet compliant frames.

Embodiments of method and apparatus for communicating control data in anasynchronous communications channel are described herein. In the abovedescription, numerous specific details are set forth (e.g., ofprocessors, interfaces, protocols, etc.) to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

Thus, embodiments of this invention may be used as or to support asoftware program executed upon some form of processing core (such as adigital signal processor (DSP) or the CPU of a computer) or otherwiseimplemented or realized upon or within a machine-readable medium. Amachine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., a DSP orother computer). For example, a machine-readable medium can include suchas a read only memory (ROM); a random access memory (RAM); a magneticdisk storage media; an optical storage media; and a flash memory device,etc. In addition, a machine-readable medium can include propagatedsignals such as electrical, optical, acoustical or other form ofpropagated signals (e.g., carrier waves, infrared signals, digitalsignals, etc.).

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. A communication system, comprising: a receiving unit; a transmittingunit operatively coupled to the receiving unit via a first channel, thetransmitting unit being configurable to transmit a first data stream tothe receiving unit in the first channel, the first data streamcontaining communications data and control data, wherein thetransmitting unit transmits the first data stream so that communicationsdata is transmitted in a grouping that complies with an asynchronousprotocol and the control data is transmitted within a segment of thefirst data stream that is specified as unused for communications dataaccording to the asynchronous protocol; wherein the receiving unitextracts communications data from the grouping in the first data streamand extracts control data from the segment in the first data stream; anda device coupled to the receiving unit, wherein the device is configuredto exchange communications data with the receiving unit over a secondchannel in a second data stream conforming to the asynchronous protocol.2. The communication system of claim 1 wherein the asynchronous protocolconforms to an Ethernet standard and the grouping is an Ethernetcompliant frame.
 3. The communication system of claim 1 wherein thesegment includes an inter-frame gap according to the asynchronousprotocol.
 4. The communication system of claim 1 wherein the segmentincludes an idle period according to the asynchronous protocol.
 5. Thecommunication system of claim 1 wherein the first channel is a freespace optical system.
 6. The communication system of claim 1 wherein thereceiving unit includes a first interface unit coupled to the firstchannel; a controller unit coupled to the first interface unit; and asecond interface unit coupled to the second channel.
 7. Thecommunication system of claim 6 wherein the controller unit includes: afirst processor to process control data; and a second processor coupledto the first processor and the first interface unit, wherein the secondprocessor is capable of transferring control data between the firstinterface unit and the first processor.
 8. The communication system ofclaim 7 wherein the second processor is further capable of transferringcontrol data between the second interface unit and the first processor.9. The communication system of claim 7 wherein the second processor isfurther capable of transferring communications data between the firstand second interface units.
 10. The communication system of claim 6wherein the first interface unit is capable of transmitting an opticalsignal via free space.
 11. The communication system of claim 10 whereinthe second channel is a wired channel.
 12. A method for use in acommunication system, the communication system having a first channel tosupport transmission according to an asynchronous protocol, the methodcomprising: detecting a first segment in a first data stream to betransmitted in the first channel, wherein the first segment is specifiedas unused for communications data according to the asynchronous protocoland wherein the first data stream includes communications datatransmitted in a grouping of the first data stream that complies withthe asynchronous protocol; transmitting the first data stream in thefirst channel, wherein the first data stream includes control data beingtransmitted within the first segment; receiving a second data streamfrom the first channel, the second data stream containing control dataand communications data, the communications data being in a firstgrouping that complies with the asynchronous protocol and the controldata being in a second segment that is specified as being unused fordata according to the asynchronous protocol; extracting control datafrom the second segment; extracting the communications data from thefirst grouping; and transmitting in a second channel the extractedcommunications data in a second grouping that complies with theasynchronous protocol.
 13. The method of claim 12 wherein theasynchronous protocol conforms to an Ethernet standard and the groupingis a frame according to the Ethernet standard.
 14. The method of claim13 wherein the first segment is an inter-frame gap according to theasynchronous protocol.
 15. The method of claim 13 wherein the firstsegment is an idle period.
 16. The method of claim 12 wherein theasynchronous protocol conforms to an Ethernet standard, the secondgrouping is a frame according to the Ethernet standard and the secondsegment is an inter-frame gap according to the Ethernet standard. 17.The method of claim 12 wherein the asynchronous protocol conforms to anEthernet standard, the second grouping is a frame and the second segmentis an idle period according to the Ethernet standard.
 18. An apparatusfor use in a communication system, the communication system having afirst channel to support transmission according to an asynchronousprotocol, the apparatus comprising: means for detecting a first segmentin a first data stream to be transmitted in the first channel, whereinthe first segment is specified as unused for data according to theasynchronous protocol; means for transmitting the first data stream inthe first channel, wherein the first data stream includes control databeing transmitted within the first segment; means for receiving a seconddata stream from the first channel, the second data stream containingcontrol data and communications data, the communications data being in afirst grouping that complies with the asynchronous protocol and thecontrol data being in a second segment that is specified as being unusedfor data according to the asynchronous protocol; means for extractingcontrol data from the second segment; means for extracting thecommunications data from the first grouping; and means for transmittingin a second channel the extracted communications data in a secondgrouping that complies with the asynchronous protocol.
 19. The apparatusof claim 18 wherein the first data stream includes communications datatransmitted in a grouping of the first data stream that complies withthe asynchronous protocol.
 20. The apparatus of claim 19 wherein theasynchronous protocol conforms to an Ethernet standard and the groupingis a frame according to the Ethernet standard.
 21. The apparatus ofclaim 18 wherein the first segment is an inter-frame gap according tothe asynchronous protocol.
 22. The apparatus of claim 18 wherein thefirst segment is an idle period according to the asynchronous protocol.